1. Field of the Invention
This invention relates to a system and method for controlling the illumination of multiple LEDs.
2. Description of the Related Art
Developments in light emitting diodes (“LEDs”) have resulted in devices that are brighter, more efficient and more reliable. LEDs are now being used in many applications that were previously the realm of incandescent bulbs; some of these include displays, automobile taillights and traffic signals. As the efficiency of LEDs improves it is expected that they will be used in most lighting applications.
Different controllers have been developed to drive multiple light sources. U.S. Pat. No. 4,962,687 to Belliveau et al. discloses a variable color lighting system which includes light fixtures controlled from a central processor unit which includes a plurality of control channels. Each light fixture includes a plurality of chromatic light sources, and the intensity of each chromatic light source is controlled in accordance with a program from the central processor over the control channels. Each light fixture is assigned a channel address, and responds only to a digital input packet from the central controller that has the same address. The digital input packet controls how the light fixture changes color intensities.
U.S. Pat. No. 6,016,038 to Mueller et al. discloses a system with pulse width modulated current control for an LED lighting assembly, where each current-controlled unit is uniquely addressable and capable of receiving illumination color information on a computer lighting network. The invention can include a binary tree network configuration of lighting units (nodes) and can comprise a heat dissipating housing made out of a heat-conductive material, for housing the lighting assembly. The heat dissipating housing contains two stacked circuit boards holding respectively the power module and the light module. The light module is adapted to be conveniently interchanged with other light modules having programmable current and hence maximum light intensity, ratings. (See also U.S. Pat. Nos. 6,150,774; 6,211,626 and 6,340,868).
U.S. Pat. No. 6,441,558 to Murtha discloses an LED luminary system for providing power to LED light sources to generate a desired light color which comprises a power supply stage configured to provide a DC current signal. A light mixing circuit is coupled to said power supply stage and includes a plurality of LED light sources with red, green and blue colors to produce various desired lights with desired color temperatures. A controller system is coupled to the power supply stage and is configured to provide control signals to the power supply stage so as to maintain the DC current signal at a desired level for maintaining the desired light output. The controller system is further configured to estimate lumen output fractions associated with the LED light sources based on junction temperature of the LED light sources and chromaticity coordinates of the desired light to be generated at the light mixing circuit. The light mixing circuit further comprises a temperature sensor for measuring the temperature associated with the LED light sources and a light detector for measuring lumen output level of light generated by the LED light sources. Based on the temperatures measured, the controller system determines the amount of output lumen that each of the LED light sources need to generate in order to achieve the desired mixed light output, and the light detector in conjunction with a feedback loop maintains the required lumen output for each of the LED light sources.
U.S. Pat. No. 6,930,452 to De Krijger et al. discloses a circuit arrangement for driving an LED array comprising red, green and blue LEDs, a control loop is added for limiting the duty cycles of the control signals for driving the red, green and blue LEDs. In case one of the duty cycles reaches the limit value, the reference signals for the red, green and blue light are decreased with the same relative amount. The color point of the light is thereby maintained, even when the efficiency of part of the LEDs decreases.